Substituted Aminobenzothiazole Derivatives of Tacrine: Synthesis and Study on Learning and Memory Impairment in Scopolamine-Induced Model of Amnesia in Rat.

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Currently, there is no conclusive cure for Alzheimer's disease (AD) and existing treatments mainly offer symptomatic relief. Dysfunction of the cholinergic system plays an important role in the pathogenesis of AD. Tacrine (1, 2, 3, 4-tetrahydroacridin-9-amine, III) was the first approved agent for the palliative therapy of AD but its use is associated with some complications. Development of novel multi target derivatives of Tacrine with lower complications is strongly warranted. In this study, new aminobenzothiazole (1-5, with many useful biological and pharmacological properties) analogues (IV-VIII) were synthesized by changing of amine moiety of III. Then, the effects of these new compounds on learning and memory impairment in scopolamine-induced model of amnesia were studied and the outcomes were compared with control and Tacrine groups in rat. The rats received Tacrine or its derivatives (IV-VIII) i.p. for two weeks at a dose of 10 mg/kg. For induction of amnesia, scopolamine at a dose of 1 mg/kg was daily administered i.p. started on day-8 till the end of the study. Behavioral experiments including Y-maze, novel object recognition (discrimination) and passive avoidance paradigms were conducted at week 2. Data analysis showed that some Tacrine derivatives, especially VII with 2-amino, 6-nitrobenzothiazole moiety, could markedly and significantly improve alternation score, discrimination ratio and step through latency compared to control and Tacrine groups. These findings indicated that some of these derivatives (especially compounds VI and VII) are capable to mitigate learning and memory deficits in scopolamine-induced model of amnesia in rats and may have potential benefit in management of patients with AD.